treewide: simplify pkgs.stdenv.lib -> pkgs.lib

The library does not depend on stdenv, that `stdenv` exposes `lib` is
an artifact of the ancient origins of nixpkgs.

nixos/tests/initrd-network.nix

@@ -1,7 +1,7 @@
 import ./make-test-python.nix ({ pkgs, lib, ...} : {
   name = "initrd-network";
 
-  meta.maintainers = [ pkgs.stdenv.lib.maintainers.eelco ];
+  meta.maintainers = [ pkgs.lib.maintainers.eelco ];
 
   machine = { ... }: {
     imports = [ ../modules/profiles/minimal.nix ];